The present invention relates generally to a mounting arrangement for securely and accurately positioning an object on a rotatable shaft and, in particular, to a tapered surface mounting structure which is especially suitable for mounting high speed rotating bodies. For example, the mounting structure of the present invention can be utilized in a rotary atomizer coater for mounting a rotary bell on an associated rotatable shaft. Examples of such rotary atomizer coaters are disclosed in U.S. Pat. Nos. 4,423,840, and 4,555,058, both of which are commonly owned by the assignee of the present application, and which are hereby incorporated by reference.
In mounting low speed rotary bodies, such as grinding wheels, it is conventional to provide the grinding wheel with a bore hole having a tapered wall which engages a cooperating tapered surface formed on a rotatable shaft in order to securely and accurately position the grinding wheel on the rotatable shaft. Such mounting arrangements are disclosed in U.S. Pat. Nos. 2,518,226 and 3,827,193. In each of these patents, the internal tapered bore of the grinding wheel is provided with a centrally disposed annular recessed portion such that only the spaced apart tapered end portions of the bore contact the cooperating tapered surface on the associated mounting shaft. Such a structure has been found to provide a suitable mounting arrangement for mounting relatively low speed rotary bodies such as grinding wheels, which are typically rotated at the synchronous speed of electric motors such as 1800 rpm or 3600 rpm.
However, in mounting relatively high speed rotary bodies, it is extremely important that the rotating mass be precisely balanced. In order to achieve proper balancing, the rotating body must be securely and precisely positioned relative to the associated rotating shaft. For example, with rotary atomizer coating equipment of the type disclosed in U.S. Pat. Nos. 9,423,840 and 4,555,058, it is extremely important that the rotary bell be precisely positioned on the rotating shaft in order to achieve proper balancing. In rotary atomizer coaters, the rotating shaft typically operates at speeds from 10,000 rpm to above 40,000 rpm and is driven by an air turbine or the like. The importance of proper alignment between the rotary bell and the shaft can be illustrated by way of the following example. For example, in a system with a 0.25 lb. (2.6 kg) object rotating at 40,000 rpm, a misalignment of 0.001 inches (0.03 mm) between the object and the shaft can cause a force of 5.68 lbs (2.6 kg) at the plane of the center of mass of the rotating object. At the very least, this imbalance places a severe strain on the turbine or spindle bearing system.
In the past, in order to achieve precise alignment between the rotary bell and the associated mounting shaft, full mating tapered surfaces have been employed between the shaft and the internal tapered bore of the rotary bell. However, such a mounting arrangement has been found to present several problems. For example, since there is substantially full contact between the male and female tapered surfaces, it has been found extremely difficult to disassemble the rotary bell from the shaft without damage to the bell. This condition is often made worse due to electrolytic corrosion between the tapered surfaces. Also, since due to normal manufacturing tolerances these facing tapered surfaces are not actually in full contact with one another along the entire length of the surfaces, this presents areas wherein the tapered surfaces are spaced apart and, in the case of a rotary atomizer coater, paint infiltration can occur to cause partial bonding between the parts. Further, during assembly, particles of dirt can become entrapped between the facing tapered surfaces to possibly interfere with the alignment of the rotary bell.